Lesser metatarsal phalangeal joint arthroscopy: anatomic description and comparative dissection

Small Joint Arthroscopy of the Foot

Recently, there have been new advances in the arthroscopic approach to small joints of the foot. This is directly related to the improvement of surgical equipment, new techniques, and publications. These improvements led to broadening indications as well as minimizing complications. Several articles recently presented the uses of arthroscopic surgery in the small joints of the foot; however, the use is still relatively limited. Arthroscopic evaluation of the small joints of the foot includes the first metatarsophalangeal, lesser metatarsophalangeal, tarsometatarsal, talonavicular, and calcaneocuboid joints as well as the interphalangeal joint to the great toe and lesser toes.

Proximal Plantar Plate of Lesser Toe Metatarsophalangeal Joint Vascular Supply

BACKGROUND

The plantar plate is a major stabilizing structure of the metatarsophalangeal (MTP) joint with instability frequently occurring after a tear or attenuation of this structure. Commonly, a McGlamry elevator is used to strip the plantar plate from the plantar surface of the metatarsal to improve exposure of the MTP joint. The anatomy of the proximal plantar plate and vascular consequence of stripping the plantar plate from the metatarsal is not yet well understood. The purpose of this study is to describe the proximal attachment of the plantar plate anatomically and quantify the relative contribution of blood supply to the proximal plantar plate from both the metatarsal and the plantar fascia.

METHODS

For anatomic evaluation, 6 lower extremity cadaver specimens without any gross evidence of foot and ankle deformity were utilized. For imaging analysis, 16 fresh frozen human adult cadaveric lower extremity specimens were used for this study, resulting in 35 MTP joints without deformity and 11 lesser MTP joints with cockup and/or crossover deformities. The specimens were prepared as described previously by Finney et al.⁵.

RESULTS

From gross anatomic dissection, the plantar plate origin consists of a stout fibrous pedicle distinct from the surrounding synovial-type tissue that firmly anchors the plantar plate to the metatarsal. Based on nano-computed tomographic imaging, an average of 63.5% of the vascular supply to the proximal portion of the plantar plate entered from the metatarsal pedicle. The remaining 36.5% of the vascular supply entered from the plantar fascia.

CONCLUSION

The proximal attachment of the plantar plate includes a stout fibrous pedicle anchoring the proximal portion of the plantar plate to the notch between the medial and lateral plantar condyles of the metatarsal head. The vascular supply of the proximal plantar plate is supplied from both the metatarsal pedicle and plantar fascia.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

Presence of Neovascularization in Torn Plantar Plates of the Lesser Metatarsophalangeal Joints

BACKGROUND

Recent surgical techniques have focused on anatomic repair of lesser toe metatarsophalangeal (MTP) plantar plate tears, yet it remains unknown whether the plantar plate has the biological capacity to heal these repairs. Therefore, a better understanding of the plantar plate vasculature in response to injury may provide further insight into the potential for healing after anatomic plantar plate repair. Recently, a study demonstrated that the microvasculature of the normal plantar plate is densest at the proximal and distal attachments. The purpose of this study was to compare the intact plantar plate microvasculature network to the microvasculature network of plantar plates in the presence of toe deformity using similar perfusion and nano-computed tomographic (CT) imaging methods.

METHODS

Seven fresh-frozen human cadaveric lower extremities with lesser toe deformities including hammertoe or crossover toe were perfused using a barium solution. The soft tissues of each foot were counterstained with phosphomolybdic acid (PMA). Then using nano-CT imaging, the second through fourth toe metatarsophalangeal joints of 7 feet were imaged. These images were then reconstructed, plantar plate tears were identified, and 11 toes remained. The plantar plate microvasculature for these 11 toes was analyzed, and calculation of vascular density along the plantar plate was performed. Using analysis of variance (ANOVA), this experimental group was compared to a control group of 35 toes from cadaveric feet without deformity and the vascular density compared between quartiles of plantar plate length proximal to distal. A power analysis was performed, determining that 11 experimental toes and 35 control toes would be adequate to provide 80% power with an alpha of 0.05.

RESULTS

Significantly greater vascular density (vascular volume/tissue volume) was found along the entire length of the plantar plate for the torn plantar plates compared to intact plantar plates (ANOVA, P < .001). For the first quartile of length (proximal to distal), the vascular density for the torn plantar plates was 0.365 (SD 0.058) compared to 0.281 (SD 0.036) for intact plantar plates; in the second quartile it was 0.300 (SD 0.044) vs 0.175 (SD 0.025); third quartile it was 0.326 (SD 0.051) vs 0.117 (SD 0.015); and fourth (most distal) quartile was 0.600 (SD 0.183) vs 0.319 (SD 0.082).

CONCLUSION

Torn plantar plates showed increased vascular density throughout the length of the plantar plate with an increase in density most notable in the region at or just proximal to the attachment to the proximal phalanx. Our analysis revealed that torn plantar plates exhibit neovascularization around the site of a plantar plate tear that does not exist in normal plantar plates.

CLINICAL RELEVANCE

The clinical significance of the increased vascularity of torn plantar plates is unknown at this time. However, the increase in vasculature may suggest that the plantar plate is a structure that is attempting to heal.

State of the Art in Lesser Metatarsophalangeal Instability

Advancements in lesser metatarsophalangeal (MTP) instability have involved the use of minimally invasive surgery techniques, synthetic augmentation of existing transfers, and use of arthroscopy for both diagnosing and addressing MTP disorder. Advances in imaging modalities, particularly MRI, have aided in diagnosing subtle instability. Clinical outcomes seem to be similar to traditional approaches as the indications and applicability continue to evolve.

Microvasculature of the Plantar Plate Using Nano-Computed Tomography

BACKGROUND:

Lesser toe plantar plate attenuation or disruption is being increasingly implicated in a variety of common clinical conditions. A multitude of surgical techniques and devices have been recently developed to facilitate surgical repair of the plantar plate. However, the microvascular anatomy, and therefore the healing potential in large part, has not been defined. We investigated the microvasculature of the plantar plate by employing a novel technique involving microvascular perfusion and nano-computed tomography (nano-CT) imaging.

METHODS:

Twelve human adult cadaveric lower extremities were amputated distal to the knee. The anterior and posterior tibial arteries were perfused with a barium solution. The soft tissues of each foot were then counterstained with phosphomolybdic acid (PMA). The second through fourth toe metatarsophalangeal (MTP) joints of 12 feet were imaged with nano-CT at 14-micron resolution. Images were then reconstructed for analysis of the plantar plate microvasculature and calculation of the vascular density along the length of the plantar plate.

RESULTS:

A microvascular network extends from the surrounding soft tissues at the attachments of the plantar plate on both the metatarsal and proximal phalanx. The midsubstance of the plantar plate appears to be relatively hypovascular. Analysis of the vascular density along the length of the plantar plate demonstrated a consistent trend with increased vascular density at approximately the proximal 29% and distal 22% of the plantar plate.

CONCLUSION:

There is a vascular network extending from the surrounding soft tissues into the proximal and distal attachments of the plantar plate.

CLINICAL RELEVANCE:

The hypovascular midportion of the plantar plate may play an important role in the underlying pathoanatomy and pathophysiology of this area. These findings may have significant clinical implications for the reparative potential of this region and the surgical procedures currently described to accomplish anatomic plantar plate repair.

Anatomy and Physiology of the Lesser Metatarsophalangeal Joints

Knowledge and command of anatomy is paramount to effectively treating disorders of the lesser metatarsophalangeal (MTP) joints. The osseous structures consist of the proximal phalanx of the toe and the metatarsal head. The soft tissues on the dorsum of the MTP joint include the joint capsule and the tendons of extensor digitorum longus and extensor digitorum brevis. The proper and accessory collateral ligaments form the medial and lateral walls and contribute to stability in the coronal and sagittal planes. The plantar plate forms the plantar border of the MTP joint and stabilizes the MTP joint against hyperextension and dorsal translation.

Small Joint Arthroscopy in the Foot

Arthroscopy has advanced in the foot and ankle realm, leading to new innovative techniques designed toward treatment of small joint abnormality. A range of abnormalities that are currently widespread for arthroscopic treatment in larger joints continues to be translated to congruent modalities in the small joints. Small joint arthroscopy offers relief from foot ailments with a noninvasive element afforded by arthroscopy. Early studies have found comparable results from arthroscopic soft tissue procedures as well as arthrodesis of the small joints when compared with the standard open approach.